Pillow: Image fixes (#6848)

* Fix return type of `Image.transform()`.
* Add animation attributes to `Image`.

stubs/Pillow/PIL/Image.pyi

@@ -110,6 +110,8 @@ class Image:
     info: dict[Any, Any]
     readonly: int
     pyaccess: Any
+    is_animated: bool  # not present on all Image objects
+    n_frames: int  # not present on all Image objects
     @property
     def width(self) -> int: ...
     @property
@@ -209,7 +211,7 @@ class Image:
         resample: _Resample = ...,
         fill: int = ...,
         fillcolor: _Color | int | None = ...,
-    ) -> None: ...
+    ) -> Image: ...
     def transpose(self, method: Literal[0, 1, 2, 3, 4, 5, 6]) -> Image: ...
     def effect_spread(self, distance: int) -> Image: ...
     def toqimage(self): ...